Purpose :
To report 5 families with Rhodopsin (RHO), GNAT1 and SCL24A1 mutations respectively where the initial diagnosis suggested a form of Congenital Stationary Night Blindness. Longitudinal follow-up revealed progression and development of symptoms and signs of a pigmentary retinopathy.

Results :
Mutations, in 5 unrelated families with congenital night blindness and initially normal day vision, were found in RHO, GNAT1 and SCL24A1. A homozygous GNAT1 mutation, c.904C>T/p.Gln302*, was identified in a patient with very late onset, 6th decade field constriction and cone ERG amplitude reduction. Two patients homozygous for SCL24A1 c.2679delT/p.Asn893fs had similar clinical features despite initially normal cone ERG responses and fundal appearances. RHO c.541G>A/p.Glu181Lys heterozygotes had a classical electronegative ERG, frequently seen in CSNB, normal fundus findings and evidence of mild cone dysfunction and field defects. RHO c.3683A>C/pGln184Pro segregated in heterozygotes with entirely normal fundal findings and full visual fields up to the 4th decade. Progressive cone dysfunction became evident in later years. RHO c.281C>T/p.Thr94Ile was found in individuals who appeared to have true CSNB. The phenotype has been non-progressive over a 20-year interval and patients, even in advanced years, only have compromised night vision.

Conclusions :
CSNB is a group of conditions that is classically characterised by life-long nyctalopia and a non-progressive phenotype. In our series of families with clinical signs and symptoms initially indicative of CSNB, affected members of four families went on to develop evidence of a progressive retinopathy. Caution in diagnosing CSNB or in favourably prognosticating is advisable especially in cases where the genotype has not been established or older affected relatives are not available for assessment.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.